1. Field of the Invention
The present invention relates to a touch panel. More specifically, the present invention relates to a capacitive touch panel to decrease resistance at an intersection where electrodes cross each other, prevent signal and sensing delays caused by resistance and thus improve touch sensitivity, and a liquid crystal display device integrated with the touch panel.
2. Discussion of the Related Art
In accordance with the recent information-dependent society, displays to visualize electric information signals have been rapidly developed. Various slim, lightweight, and low-power flat display devices are commonly used as alternatives to conventional cathode ray tubes (CRTs).
Examples of flat display devices include liquid crystal displays (LCDs), plasma display panels (PDPs), field emission displays (FEDs), electroluminescent displays (ELDs) and the like. These flat display devices necessarily require a flat display panel to realize an image wherein the flat display panel has a structure in which a pair of transparent insulating substrates is joined such that an inherent luminous or polarized material layer is interposed between the substrates. Among flat display devices, liquid crystal display devices control light transmittance of liquid crystals using an electric field to display an image. For this purpose, an image display device includes a display panel including liquid crystal cells, a backlight unit to irradiate light to the display panel and an operation circuit to operate liquid crystal cells.
The display panel is formed such that a plurality of gate lines cross a plurality of data lines to define a plurality of unit pixel regions. Each pixel region includes a thin film transistor array substrate and a color filter array substrate facing each other, a spacer interposed between the two substrates to maintain a predetermined cell gap, and a liquid crystal filled in the cell gap.
The thin film transistor array substrate includes a plurality of gate lines and a plurality of data lines, a thin film transistor formed as a switching device at each intersection between the gate line and the data line, a pixel electrode arranged in each liquid crystal cell and connected to the thin film transistor, and an orientation film coated on the resulting structure. The gate lines and data lines receive signals through respective pad portions from operation circuits.
In response to scan signals supplied to the gate lines, the thin film transistor transfers pixel voltage signals supplied to data lines to the pixel electrode.
In addition, the color filter array substrate includes color filters arranged in respective liquid crystal cells, a black matrix to partition the color filters and reflect external light, a common electrode to supply a reference voltage to the liquid crystal cells, and an orientation film coated on the resulting structure.
The thin film transistor substrate and the color filter array substrate thus separately formed are arranged and then joined such that the two substrates face each other, liquid crystal is injected into a region provided between the substrates, and the region is sealed, to complete fabrication of the liquid crystal display device.
There is an increasing need for providing a touch panel wherein a portion that is touched by the hand or separate input means is sensed, and additional information can be transferred in response to the touch, to the liquid crystal display device thus fabricated. Such a touch panel is adhered to the external surface of a liquid crystal display.
Depending on the touch sensation type, touch panels are classified into resistive touch panels, capacitive touch panels and infrared (IR) touch panels. Owing to factors such as convenience of fabrication and sensitivity, capacitive touch panels have attracted considerable attention.
Hereinafter, a capacitive touch panel according to the present invention will be described with reference to the annexed drawings in detail.
FIG. 1 is a plan view illustrating an electrode intersection of conventional touch panel.
As shown in FIG. 1, the conventional capacitive touch panel includes a plurality of first electrodes 13 and a plurality of second electrodes 14 arranged in different directions on a substrate 10.
The second electrodes 14 are formed by connecting connection portions with a small width to diamond patterns connected in a longitudinal direction, and the first electrode 13 and the second electrode 14 are branched into each other at the intersection therebetween. At the second electrode 14, the diamond patterns are integrated with the connection portions and the first electrode 13 is formed with diamond patterns spaced from one another.
An insulating film 12 is formed under the first electrodes 13 and the second electrodes 14, a connection metal 11 is further formed on the substrate 10 in a region provided between the divided first electrodes 13. Accordingly, the connection metal 11 electrically contacts the first electrode 13 at a contact hole 12a to partially expose the connection metal 11, thus allowing common signals to be applied to the separated first electrodes 13.
The first and second electrodes 13 and 14 are transparent electrodes.
In this instance, the second electrode 14, except for the connection portion, has a diamond shape, and in practical application, the connection portion to connect diamond patterns of the second electrode 14 has a considerably small width and thus considerably large resistance.
The first electrodes 13 are connected through the connection metal 11 composed of a metal. For this reason, there is a great difference in resistance between the connection portion of the first electrode 13 and the connection portion of the second electrode 14 due to differences in material and structure therebetween. The great difference in resistance causes deterioration in application of operation voltage due to RC delay, taking into consideration the fact that electrodes include a plurality of these connection portions, thus the deterioration in sensitivity of touch. Specifically, resistance at the connection portion of the second electrode 14 corresponds to 20% or higher of resistance of one diamond pattern, which is high when compared to its area.
In addition, the connection portion of the second electrode 14 having a high resistance composed of a transparent electrode material may be readily damaged during static electricity testing and thus be shorted or seriously damaged. In this instance, the use of the panel may be impossible.
The conventional touch panel has the following disadvantages.
One of the first electrode and the second electrode which cross each other are arranged in one direction and the other thereof are spaced from one another at the connection portion, and a second bridge electrode is provided under the electrode, to connect the electrodes.
In this instance, the first and second electrodes are composed of a transparent electrode material and the electrodes arranged lengthways in one direction have a small width and thus a considerably high resistance at the connection portion.
The connection portion having a high resistance causes RC delay of electrodes and deterioration in sensitivity and operation voltage and inhibits sensitive touch detection.
In addition, the connection portion of the electrodes having a high resistance composed of a transparent electrode material may be readily damaged upon static electricity tests and be thus shorted or seriously damaged. In this instance, the use of the panel may be impossible.